A method for preparing a recombinant compact tensile specimen

Abstract

The present invention discloses a preparation method of a recombined compact tension specimen, comprising the following steps: 1) preparing a specimen for a target material and spraying speckles on the surface of the specimen; 2) conducting a fracture toughness test on the specimen, and during the fracture toughness test, measuring the specimen by using a full-field strain measurement system; 3) determining a plastic strain region on the surface of the specimen according to the measurement result of the full-field strain measurement system and excising the plastic strain region, and retaining the non-plastic strain regions on both sides of the specimen to obtain a recombined block; 4) welding the recombined block with auxiliary materials to obtain the recombined compact tension specimen. The preparation method of the recombined compact tension specimen of the present invention, through reasonable recombination means and verification means, enables the performance of the recombined specimen to be similar to that of the original specimen; and the non-plastic deformation regions (recombined blocks) after the fracture toughness test can be recombined into two or more specimens, increasing the material utilization rate by three times or more.

Description

Technical Field

[0001] The present invention belongs to the technical field of specimen preparation and testing, and particularly relates to a method for recombining compact tension (CT) specimens of fracture toughness, which is applicable to the recombination of CT specimens of fracture toughness for materials of reactor pressure vessels in nuclear power plants. Background Art

[0002] The reactor pressure vessel (RPV) is the primary circuit pressure boundary of a pressurized water reactor nuclear power plant and cannot be replaced during the service life of the nuclear power plant, which affects and limits the service time of the nuclear power plant. The service environment of the RPV is extremely harsh, being exposed to high temperature, high pressure, and intense neutron irradiation for a long time. Moreover, low-alloy ferritic steel is mostly used for RPV materials, which has a potential risk of low-temperature brittle fracture under neutron irradiation conditions.

[0003] In order to monitor the irradiation embrittlement of the RPV, irradiation surveillance tubes are usually suspended on the inner wall of the RPV, and specimens such as tensile, impact, and compact tension (CT) specimens are loaded in the surveillance tubes to test the mechanical properties after irradiation, so as to evaluate the structural integrity of the RPV.

[0004] However, due to the limited space in the irradiation surveillance tube, the number of specimens that can be placed is limited, and the obtained test data are also limited. On the other hand, when a nuclear power plant needs to obtain material property data monitored to the neutron fluence at the end of the service life of 60 years or even 80 years for life extension, there may be a situation of insufficient reserved archival materials or too long irradiation time for unirradiated materials. The development of specimen recombination technology is considered to be the most promising effective solution to solve the above problems.

[0005] Specimen recombination technology is a specimen preparation technology in which other auxiliary materials with similar properties are connected around a small amount of research materials and then processed into composite specimens (standard-size or non-standard-size specimens) that can meet the geometric dimension requirements. The research materials can be taken from irradiated surveillance specimens, thereby greatly increasing the irradiated performance data. Moreover, when re-monitoring during life extension with irradiated materials, the re-irradiation time can be greatly reduced, and performance data can be obtained as soon as possible. Summary of the Invention

[0006] In view of this, in order to overcome the defects of the prior art, the purpose of the present invention is to provide a preparation method for recombining compact tension specimens, which can effectively improve the utilization rate of materials and ensure the accuracy of test results.

[0007] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0008] A preparation method for recombining compact tension specimens includes the following steps:

[0009] 1) Prepare a specimen for the target material and spray speckles on the surface of the specimen;

[0010] 2) Conduct a fracture toughness test on the specimen. During the fracture toughness test, use a full-field strain measurement system to measure the specimen.

[0011] 3) According to the measurement results of the full-field strain measurement system, determine the plastic strain region on the surface of the specimen and cut it off, retain the non-plastic strain regions on both sides of the specimen and obtain a recombined block.

[0012] 4) Weld the recombined block with auxiliary materials to obtain the recombined compact tension specimen.

[0013] According to some preferred implementation aspects of the present invention, when determining the plastic strain region on the surface of the specimen, finite element simulation needs to be carried out, and it is necessary to ensure that the error between the measurement result of the full-field strain measurement system corresponding to the plastic strain region and the maximum strain result obtained by finite element simulation is kept within 10%.

[0014] According to some preferred implementation aspects of the present invention, when determining the plastic strain region on the surface of the specimen, microhardness testing needs to be carried out on the obtained plastic strain region to ensure that the hardness of the plastic strain region is greater than that of the non-plastic strain region. Due to plastic hardening, the microhardness of the plastic strain region is relatively high, so this method can determine the rationality of the full-field strain measurement results.

[0015] That is, the determination of the size of the plastic strain region is first determined by the measurement results of the full-field strain measurement system, and then first verified according to finite element simulation. It is necessary to ensure that the error between the maximum strain results obtained by the two methods is kept within 10%. Finally, the final verification is carried out through microhardness testing to ensure that the hardness of the plastic strain region is greater than that of the recombined block.

[0016] According to some preferred implementation aspects of the present invention, there is a weld between the non-plastic strain region in the recombined compact tension specimen and the auxiliary material, and the width of the weld is less than 1 mm. The smaller the width of the weld, the better, and the smaller the impact on the test results of the recombined specimen.

[0017] According to some preferred implementation aspects of the present invention, the welding is carried out by electron beam welding, and the parameters are voltage 50 - 100 kV, current 400 - 800 mA, and welding speed 800 - 1200 mm / min. The weld width obtained by electron beam welding is smaller, ensuring the requirement that the weld width is less than 1 mm. And microhardness testing and microstructure observation are carried out on the obtained recombined compact tension specimen to determine its weld width.

[0018] According to some preferred implementation aspects of the present invention, the welding parameters are determined through the following steps: Select a raw material of the same material as the target material, prepare a recombined compact tension specimen from the raw material according to the steps 1) to 4), conduct a fracture toughness test on the recombined compact tension specimen of the raw material and the raw material that has not undergone the steps 1) to 4). If the error between the test results of the two is within 10%, the welding parameters meet the conditions.

[0019] According to some preferred implementation aspects of the present invention, the welding is carried out under vacuum conditions. That is, when performing electron beam welding, the entire welding base is placed into the vacuum system to carry out vacuum electron beam welding to prevent oxidation of the material during electron beam welding.

[0020] According to some preferred implementation aspects of the present invention, the material of the auxiliary material is the same as that of the target material to ensure that the performance of the recombined specimen is similar to that of the original specimen; the auxiliary material includes a first recombined material, a protective material, a second recombined material, and a recombined protective material that are respectively arranged around the recombined block in sequence. The auxiliary material is used to be spliced with the recombined block to form a recombined compact tension specimen.

[0021] According to some preferred implementation aspects of the present invention, during welding, a positioning groove is opened on the welding base, and a first arc starting block, a limiting block, the recombined block, the auxiliary material, a second arc starting block, and a third arc starting block are placed in the positioning groove; the first recombined material and the second recombined material are respectively located on both sides in the thickness direction of the recombined block, the protective material and the recombined protective material are respectively located on both sides in the length direction of the recombined block, and the limiting block is located between the first arc starting block and the protective material; the first arc starting block is arranged corresponding to the length direction of the protective material, the second arc starting block is correspondingly arranged at the connection between the first recombined material and the recombined protective material, and the third arc starting block is correspondingly arranged at the connection between the second recombined material and the recombined protective material.

[0022] According to some preferred implementation aspects of the present invention, the size of the limiting block is larger than the thickness of the protective material; the sizes of the second arc starting block and the third arc starting block are larger than the distance between the first recombined material or the second recombined material and the recombined protective material.

[0023] A protective material is spliced above the recombinant block in the length direction to prevent damage to the recombinant block during the arc starting and arc extinguishing of electron beam welding; a recombinant protective material is spliced below the recombinant block in the length direction, which serves as both a recombinant material and a protective material at the same time; a limiting block is placed above the protective material in the length direction to limit the recombinant block and the recombinant materials on both sides thereof and prevent dislocation during welding; a first arc starting block is placed above the limiting block in the thickness direction, and a side arc starting block is placed outside the recombinant material for arc starting and arc extinguishing of electron beam welding; the recombinant material, the protective material and the arc starting block are all loaded into the welding base to limit during electron beam welding and ensure the welding quality.

[0024] According to some preferred implementation aspects of the present invention, the sprayed speckles are formed by first spraying a layer of white primer on the surface of the specimen, and then dot-spraying black paint on the white primer to form speckles.

[0025] Due to the adoption of the above technical solutions, compared with the prior art, the beneficial effects of the present invention are as follows: The preparation method of the recombinant compact tension specimen of the present invention makes the performance of the recombinant specimen similar to that of the original specimen through reasonable recombination means and verification means; and the non-plastic deformation area (recombinant block) after the fracture toughness test can be recombined into two or more specimens, increasing the material utilization rate by three times or more. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 It is a schematic structural diagram of the recombinant compact tension specimen during welding in a preferred embodiment of the present invention;

[0028] Wherein: welding base - 1, upper arc starting block - 2, limiting block - 3, protective material - 4, recombinant material - 5, research material - 6, recombinant protective material - 7, side arc starting block - 8. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0030] As Figure 1 shown, the method for preparing a recombined compact tension specimen in this embodiment includes the following steps:

[0031] Step 1:

[0032] Prepare a specimen of the target material into a specimen for fracture toughness test by a conventional method, and spray speckles on the surface of the specimen.

[0033] Spraying speckles is to first spray a layer of white primer on the surface of the specimen, and then dot-spray black paint on the white primer to form speckles, which cooperate with the measurement of the subsequent full-field strain measurement system.

[0034] Step 2:

[0035] Conduct a fracture toughness test on the specimen, and during the fracture toughness test, measure the specimen using a full-field strain measurement system.

[0036] Step 3:

[0037] According to the measurement results of the full-field strain measurement system, determine the plastic strain region on the surface of the specimen and cut it off, retain the non-plastic strain regions on both sides of the specimen and obtain a recombined block.

[0038] Meanwhile, when determining the plastic strain region on the surface of the specimen, finite element simulation needs to be carried out, and it is necessary to ensure that the error between the measurement result of the full-field strain measurement system corresponding to the plastic strain region and the maximum strain result obtained by finite element simulation is kept within 10%.

[0039] Meanwhile, when determining the plastic strain region on the surface of the specimen, microhardness testing needs to be carried out on the obtained plastic strain region to ensure that the hardness of the plastic strain region is greater than that of the non-plastic strain region. Due to plastic hardening, the microhardness of the plastic strain region is relatively high, so this method can determine the rationality of the full-field strain measurement results.

[0040] That is, the determination of the size of the plastic strain region in this step is first determined by the measurement results of the full-field strain measurement system, secondly, it is initially verified according to finite element simulation, and it is necessary to ensure that the error between the maximum strain results obtained by the two methods is kept within 10%. Finally, the final verification is carried out through microhardness testing to ensure that the hardness of the plastic strain region is greater than that of the recombined block.

[0041] Step 4:

[0042] Prepare auxiliary materials. The material of the auxiliary materials is the same as that of the target material to ensure that the performance of the recombined specimen is similar to that of the original specimen. The auxiliary materials include a first recombined material, a protection material, a second recombined material, and a recombined protection material that are sequentially arranged around the recombined block. The auxiliary materials are used to be spliced with the recombined block to form a recombined compact tensile specimen.

[0043] At the same time, in order to protect the recombined block during the welding process, a first arc starting block, a limiting block, a recombined block, auxiliary materials, a second arc starting block, and a third arc starting block also need to be set. A protection material is spliced above the length direction of the recombined block to prevent damage to the recombined block during the arc starting and arc extinguishing of electron beam welding; a recombined protection material is spliced below the length direction of the recombined block, which serves as both a recombined material and a protection material at the same time; a limiting block is placed above the length direction of the protection material to limit the recombined block and the recombined materials on both sides of it and prevent misalignment during the welding process; a first arc starting block is placed above the thickness direction of the limiting block, and a side arc starting block is placed outside the recombined material for arc starting and arc extinguishing of electron beam welding; the recombined materials, the protection material, and the arc starting blocks are all installed in the welding base to limit during electron beam welding and ensure the welding quality.

[0044] As Figure 1 shown, the first recombined material and the second recombined material are respectively located on both sides of the recombined block in the thickness direction, the protection material and the recombined protection material are respectively located on both sides of the recombined block in the length direction, and the limiting block is located between the first arc starting block and the protection material; the first arc starting block is arranged corresponding to the length direction of the protection material, the second arc starting block is correspondingly arranged at the connection between the first recombined material and the recombined protection material, and the third arc starting block is correspondingly arranged at the connection between the second recombined material and the recombined protection material. The size of the limiting block is larger than the thickness of the protection material; the sizes of the second arc starting block and the third arc starting block are larger than the distance between the first recombined material or the second recombined material and the recombined protection material.

[0045] Weld the recombined block and the auxiliary materials to obtain a recombined compact tensile specimen. There is a weld between the non-plastic strain region in the recombined compact tensile specimen and the auxiliary materials, and the width of the weld is less than 1 mm.

[0046] The welding is carried out by electron beam welding, and the parameters are voltage 50 - 100 kV, current 400 - 800 mA, and welding speed 800 - 1200 mm / min. The weld width obtained by electron beam welding is smaller, which ensures the requirement that the weld width is less than 1 mm. And carry out microhardness testing and microstructure observation on the obtained recombined compact tensile specimen to determine its weld width.

[0047] The welding parameters are determined through the following steps: Select the original material with the same material as the target material, prepare the recombined compact tension specimen from the original material according to steps 1) to 4), conduct a fracture toughness test on the recombined compact tension specimen of the original material and the original material that has not undergone steps 1) to 4). If the error between the test results of the two is within 10%, the welding parameters meet the conditions.

[0048] During welding, a positioning groove is opened on the welding base, and the first arc starting block, the limiting block, the recombined block, the auxiliary material, the second arc starting block, and the third arc starting block are placed in the positioning groove; and the whole is placed in a vacuum system for recombined welding. That is, during electron beam welding, the entire welding base is loaded into the vacuum system to carry out vacuum electron beam welding to prevent the oxidation of the material during electron beam welding.

[0049] The preparation method of the recombined compact tension specimen of the present invention effectively determines the plastic deformation region in the fracture toughness test of the CT specimen through full-field strain testing, finite element simulation, and microhardness. The recombined specimen is prepared by vacuum electron beam welding of the auxiliary material. The error between the fracture toughness test results of the recombined specimen and the results of the original research material is within 10%, effectively increasing the material utilization rate by 3 times. In the present invention, the setting of the base and the material for the welding process makes the recombined welding method simple and stable, with high welding quality and a weld width less than 1 mm, and can realize the specimen recombination of the reactor pressure vessel material in a nuclear power plant, effectively improving the material utilization rate.

[0050] The above embodiments are only used to illustrate the technical concept and characteristics of the present invention, and their purpose is to enable those familiar with this technology to understand the content of the present invention and implement it accordingly, and cannot be used to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a recombinant compact tension specimen, characterized in that, It includes the following steps: 1) Prepare a specimen for the target material and spray speckles on the surface of the specimen; 2) Conduct a fracture toughness test on the specimen. During the fracture toughness test, use a full-field strain measurement system to measure the specimen; 3) Determine the plastic strain region on the surface of the specimen according to the measurement results of the full-field strain measurement system and cut it off. Retain the non-plastic strain regions on both sides of the specimen to obtain a recombined block; 4) Weld the recombined block with an auxiliary material to obtain the recombined compact tension specimen; When determining the plastic strain region on the surface of the specimen, finite element simulation is required, and it is necessary to ensure that the error between the measurement result of the full-field strain measurement system corresponding to the plastic strain region and the maximum strain result obtained by finite element simulation is within 10%. When determining the plastic strain region on the surface of the specimen, it is necessary to conduct a microhardness test on the obtained plastic strain region to ensure that the hardness of the plastic strain region is greater than that of the non-plastic strain region; The welding is carried out by electron beam welding, and the parameters are voltage 50 - 100 kV, current 400 - 800 mA, and welding speed 800 - 1200 mm / min.

2. The preparation method according to claim 1, characterized in that, There is a weld seam between the non-plastic strain region in the recombined compact tension specimen and the auxiliary material, and the width of the weld seam is less than 1 mm.

3. The preparation method according to claim 2, characterized in that, The welding parameters are determined through the following steps: Select a raw material with the same material as the target material. Prepare a recombined compact tension specimen from the raw material according to the steps 1) - 4). Conduct a fracture toughness test on the recombined compact tension specimen of the raw material and the raw material that has not undergone the steps 1) - 4). If the error between the test results of the two is within 10%, the welding parameters meet the requirements.

4. The preparation method according to claim 1, characterized in that, The welding is carried out under vacuum conditions.

5. The preparation method according to claim 1, characterized in that, The material of the auxiliary material is the same as that of the target material; the auxiliary material includes a first recombined material, a protective material, a second recombined material, and a recombined protective material that are sequentially arranged around the recombined block.

6. The preparation method according to claim 5, characterized in that, During the welding, a positioning groove is opened on the welding base, and a first arc starting block, a limiting block, the recombined block, the auxiliary material, a second arc starting block, and a third arc starting block are placed in the positioning groove; the first recombined material and the second recombined material are respectively located on both sides of the recombined block in the thickness direction, the protective material and the recombined protective material are respectively located on both sides of the recombined block in the length direction, and the limiting block is located between the first arc starting block and the protective material; the first arc starting block is arranged corresponding to the length direction of the protective material, the second arc starting block is arranged corresponding to the connection between the first recombined material and the recombined protective material, and the third arc starting block is arranged corresponding to the connection between the second recombined material and the recombined protective material.

7. The preparation method according to claim 6, characterized in that, The size of the limiting block is larger than the thickness of the protective material; the sizes of the second arc starting block and the third arc starting block are larger than the distance between the first recombined material or the second recombined material and the recombined protective material.

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